Inbreeding: This is basically keeping a strain pure. The fish are kept closely related and brother and sister, father and daughter are routinely bred. A breeder will do this sometimes to fix a trait, such as a particular colour or shape. Mostly, you take the best male and female from the drop and breed them. Doing this can provide beautiful fish for years, provided the fish that you start out with are quality and you are lucky enough to choose not only the most attractive fish, but to pick fish as breeders that do not have an invisible weakness-for these will show up in the form of genetic defects, often looked upon as simply the result of "too much inbreeding". Take great care in choosing breeders; many times a strong body is the most desirable trait to keep an inbred line strong. Line Breeding/Line Crossing: This method is also a form of inbreeding, however here you start by keeping the fry from two females (either from your new trio or chosen fry from a drop) separate, so that they form two distinct lines. Since you cannot mix batches, this takes more tanks. It is best to choose breeders differently for each line; for instance, in one line, you may pursue a large body mass, and with the other, you may concentrate on finnage. The purpose is to help maintain your established strain, since each line becomes distinct and more distantly related; also, you can have your own two lines to cross occasionally. When you want to increase the size in your fish, for instance, or make an outcross to avoid too much inbreeding, taking someone else's line to do this with is risky and you may loose the traits in your line that you have worked hard to achieve, as well as loosing the homozygous quality of your guppies. Out Crossing: This is the opposite of inbreeding - the mating of fish that are unrelated to other. This creates what is called a "hybrid" guppy. "Hybrid" vigor may be seen in such fish-outstanding size, colour, and health. The genetic patterns of the parents are scrambled/mixed up, and such fish may be good for show but not for breeding. An outcross with a fish that itself is only a few generations ahead of an outcross may produce beautiful fish for a few generations, but the loose gene patterns will turn them eventually into a fish resembling the small, original wild guppy usually sold as feeders in pet stores. Although this is, of course, how new strains are produced, it takes much time and knowledge of genetics to create a pure strain. Thus, it is not advisable for the novice to attempt an out cross in order to fix a strain. Most breeders stick with line breeding and do their best to choose fish to breed with that have the characteristics which they think will improve their lines, while keeping their guppies breeding pure. It's important to remember that guppies react differently with various methods of care, water conditions, and breeding methods. What works for one person may not work for you when trying to breed the exact same line of fish. Every strain varies in it's own needs and rate of development, as well. It takes years of attentive care and analyzing breeding techniques to find out just what works for you and your guppies. This is what makes guppy breeding the fascinating hobby it is!
Choosing the females may be difficult since they show little of the genetic make-up that they carry. Females should have a nicely-shaped body that is also large and stout with thick caudal peduncles. Their caudals should have even colouration and shape. Colour is not really important. Overly coloured females do not generally throw very good males in their drops. Females should be used at about 3 to 4 months of age. Males should, of course, show all the favourable characteristics you are trying to obtain. This is will likely include a nicely shaped caudal with good colouration and a dorsal fin that matches closely. They should have a good body shape and look strong and energetic....
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